The present invention relates to an optical printing head, including an arrangement of light switching elements, of the type employed in parallel printers for the line-by-line recording of picture and text information. More particularly, the present invention relates to an improved optical printing head of the above described type wherein a plurality of juxtaposed light switching elements receive light by means of cross section converters which are in communication with a light source, and the light switching elements can be actuated such that the light is transmitted in dots by means of objective lenses along the length of a line to be recorded on a photosensitive record carrier.
Data processing systems require fast printers to convert electrical input signals into visible displays that can be easily read in a print-out. For this purpose, printers equipped with optical printing heads have been used with success. For example, an optical printing device including a photosensitive record carrier, photopaper or an intermediate record carrier and an electrically controllable optical component having picture dot elements for blocking the flow of light or permitting it to pass is disclosed in German Offenlegungsschrift [laid-open patent application] No. 2,557,254, published June 30, 1977.
An optical printer having a magnetically controllable optical component is disclosed in German Offenlegungsschrift No. 2,812,206, published Oct. 4, 1979. It is based on an integrated light modulation matrix which requires neither the deflection of a light beam nor electrostatic charges for the actual printing process. Such an integrated light modulation matrix is disclosed in German Offenlegungsschrift No. 2,606,596, published Aug. 25, 1977.
The operation of that matrix is based on light modulation by means of magneto-optical storage layers, such as, for example, iron garnet layers. Such layers include a uniform arrangement of light switching elements which are switched purely electronically by means of vapor-deposited layers of conductor paths and resistors. With high integration density, it is possible to construct line-by-line switching, light switching components including more than one thousand elements. These light switching elements are disposed between a constant light source and a photosensitive record carrier and can be controlled by a character generator in such a manner that the light constantly radiated by the light source can be blocked or passed as required at the locations of predetermined character raster dots.
In order to be able to form a single straight print line on the photosensitive surface, a plurality of light switching elements which are arranged in a row transversely to the direction in which the record carrier is transported, are required. Below the light switching elements, and between these elements and the record carrier, which may for example, be a photoconductive drum, an optical system is provided which serves to image the light switching elements on the record carrier.
To obtain a precisely aligned printed line on the record carrier without visible transitions between images of the individual switching elements, adjustment must be possible. For this purpose, one known arrangement adjusts each component composed of one light switching element and one objective lens. Since such a component is relatively large and displacement must remain within very narrow limits, such adjustment is very time-consuming and costly.
Moreover, German patent application No. 3,214,519 corresponding to U.S. application Ser. No. 06/486,937, filed Apr. 20, 1983 by H. Behrens et al., discloses a printer having an optical printing head for the line-by-line recording of graphic and text information, wherein it is proposed to arrange and attach the light switching elements by positioning and fastening an edge of a light switching element body so that it is parallel to the actual switching line. The light switching elements are here inserted individually into the printing head. Their image, however, is adjusted by displacing the objective lenses relative to one another. This arrangement has found acceptance in practice because the light switching elements employed here are provided with a light coupling member made of glass onto which a light coupling plug can be placed without requiring alignment.